[CMake] Tell libc++ that we're using compiler-rt on Apple platforms

Reviewers: beanz, arphaman, EricWF

Subscribers: dberris, mgorny, jkorous, dexonsmith, jdoerfert, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D58921

llvm-svn: 355927

Author: ldionne

clang/cmake/caches/Apple-stage2.cmake

@@ -38,6 +38,7 @@ set(CMAKE_BUILD_TYPE RelWithDebInfo CACHE STRING "")
 set(LIBCXX_INSTALL_LIBRARY OFF CACHE BOOL "")
 set(LIBCXX_INSTALL_HEADERS ON CACHE BOOL "")
 set(LIBCXX_INCLUDE_TESTS OFF CACHE BOOL "")
+set(LIBCXX_USE_COMPILER_RT ON CACHE BOOL "")
 set(LLVM_LTO_VERSION_OFFSET 3000 CACHE STRING "")
 
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